Lactic acid bacteria are conventionally used for manufacturing fermented food products, in particular dairy products.
It has been reported that, besides their nutrient qualities, some of these food products exert beneficial effects on health; these properties have been the subject of particular interest for some decades, and many investigations have been carried out with the aim of confirming them and of defining more precisely the role played by lactic ferments.
It has thus been shown that some lactic acid bacteria, in particular among lactobacilli and bifidobacteria, improve immunity against infectious agents [PAUBERT-BRAQUET et al., Int. J. Immunother. 11, 153–161 (1995); KAILA et al., Dis. Child. 72, 51–53 (1995); HUDAULT et al. Appl. Environ. Microbiol. 63, 513–518 (1997)], and also have anti-tumour activity [HAYATSU et al. Cancer Lett. 73, 173–179 (1993); HOSONO et al. Agric. Biol. Chem. 54, 1639–1643 (1990); HOSODA et al. J. Dairy Sci. 75, 976–981 (1992)].
These effects have, in particular, been attributed to an action on the composition of the intestinal microflora, to the detriment of pathogenic microorganisms, and/or to a more direct action on the immune system, manifesting itself in particular through an increase in the level of cytokines which activate the immune system, such as γIFN of interleukins, and also an increase in the number of activated cells involved in the specific or non-specific immune response, such as lymphocytes and macrophages, and an increased secretion of immunoglobulins [PERDIGON et al., Int. J. Immunother. 9, 29–52, PORTIER et al., Int. J. Immunother. 9, 217–224 (1993); SOLIS PEREYRA and LEMONNIER, Nutr. Research 13, 1127–1140 (1993)]; DE SIMONE et al., Int. J. Immunother. 9, 23–28 20 (1993); PERDIGON et al., J. Dairy Res. 61, 553–562 (1994); SCHIFFRIN et al. J. Dairy Sci. 78, 491–497 (1995)].
However, it appears that the beneficial effects induced by lactic acid bacteria may vary depending on the origin of the pathological condition concerned, the bacterial species and/or strain used and the conditions of administration. In order to more successfully adapt the use of these bacteria, or of the products containing them, in the context of treating or of preventing specific pathological conditions, and in order to be in a position to select the bacteria which are the most suitable for the desired use, it is therefore necessary to more clearly understand the mechanisms by which their effects are exerted.
The inventors have undertaken to study the effect, on the intestinal mucous membrane, of lactic acid bacteria of the Lactobacillus casei group; with the same, they have chosen the L. casei strain DN 114001. This strain is described in PCT application WO 96/20607 in the name of: COMPAGNIE GERVAIS DANONE, and was deposited on 30 Dec. 1994, with the CNCM (Collection Nationale de Cultures de Microorganismes [National Collection of Microorganism Cultures]) held by the Institut Pasteur, 25 rue du Docteur Roux, in Paris, under the number I-1518, and the beneficial properties thereof in the context of treating diarrhoea have been shown.
The inventors have studied the effect, in vitro of this L. casei strain on the production of mediators of non-specific immunity (pro-inflammatory cytokines and nitric oxide), by enterocytes in culture.
These cell lines, which are derived from human intestinal epithelium, constitute a model for studying the response of the latter to an attack, which may be infectious or otherwise. This response manifests itself in particular through the production of pro-inflammatory cytokines (mainly IL-1, IL-6, TNF-α), and of nitric oxide (NO) generated by an inducible isoform of NO synthase (iNOS). Nitric oxide participates, through its antimicrobial properties, in the defence against pathogenic microorganisms and, when it is produced in a small amount, in the production of the intestinal mucous membrane. However, at high dose, it decreases the viability of the epithelial cells and contributes to the establishment and to the maintaining of a chronic inflammatory state [ALICAN and KUBES, Am. J. Physiol. 270, G225–237, (1996); TEPPERMAN et al., J. Pharmacol. Exp. Ther., 271, 1477–1482, (1994)]. The production of NO by enterocytes in culture can be induced with pro-inflammatory cytokines [VALETTE et al., Br. J. Pharmacol., 121, 187–182 (1997); KOLIOS et al., Br. J. Pharmacol., 116, 2866–2872 (1995)], and also with lipopolysaccharide (LPS) toxins of certain gram-negative bacteria (TEPPERMAN et al., 1994, abovementioned publication). Recent studies [SALZMAN et al., Gastroenterology, 114, 93–102, (1998); WITTHOFT et al., Am. J. Physiol., 275, G564–571, (1998)] indicate that Escherichia coli, Salmonella dublin, and Shigella flexneri enteropathogenic bacteria induce the expression of iNOS and the production of NO in enterocyte cultures which may or may not have been preactivated with pro-inflammatory cytokines.
The inventors have now noted that in the case of their experiments with L. casei, the action on the production of pro-inflammatory cytokines and of NO varies according to the activation state of the enterocytes. Specifically, when the cells are in their basal state, no effect of L. casei is observed; when they are activated by adding pro-inflammatory cytokines (which reproduces the conditions of an attack, which may be infectious or otherwise), a low production of NO and of TNF is observed; this response to the attack is very significantly increased by adding L. casei. Finally, in the case of cells hyperactivated by adding inflammatory cytokines and LPS (which reproduces the conditions of a pathogenic inflammatory state), a decrease in the production of NO and of TNF, which is restored to an optimum level, is, on the contrary, observed.
It appears, therefore, that this L. casei strain promotes an adaptive response of cells to an attack, via the modulation of factors involved in non-specific immunity.